Larvae of the black soldier fly (BSF; Hermetia illucens; as utilized herein, BSFs means black soldier flies) are well suited to converting organic waste products, such as fruit and vegetable matter (including coffee pulp), meat and fish, bread and grains, and manures, into market-valuable products, such as livestock (terrestrial or aquatic) feed or feed ingredients, pet food, food stuffs for human consumption, and plant growth supplements. Advantages of BSFs include the following: (i) BSFs are indigenous to the Americas and are now found in many parts of the world; (ii) BSF larvae grow on a wide variety of organic waste products; (iii) BSF larvae and prepupae are high in protein and fatty acid content and self-harvesting; (iv) BSF adults do not need food and are therefore are not known as a disease vector; (v) BSF larvae demonstrate anti-pathogenic qualities (Erickson, et al. 2004; Liu, et al. 2008); and (vi) BSF larvae produce stable colonies because they deter colonization from other insect species (Bradley and Sheppard, 1984) and can survive in a variety of environmental conditions.
As a member of the Family Stratiomyidae, the BSF goes through full metamorphosis during its lifespan. This includes the egg, larval, pupae and adult life cycle stages. Larvae will hatch from the egg stage after 48-72 hours and go through five instars (larval stages) before reaching the pupae stage. The first instar (L1) will molt into the second instar (L2) within 4-5 days and generally reach the pupae stage within a further 12-30 days, and for example, within 12-18 days, depending on temperature, humidity, type of feed, quantity of feed, frequency of feeding, mixture of feed ingredients, moisture of feed, starter diet, finishing diet and consistency of feed. Between the fifth instar (L5) and the pupae stage is the prepupae stage, where BSF larvae seek a drier environment, for example an environment that is less saturated or less than 100% moisture, to complete the metamorphosis stage of its life cycle. Accordingly, prepupae will crawl away from their “juvenile” feeding grounds, i.e., the organic wastes. This dispersal behavior translates into a “self-harvesting” mechanism which allows for a convenient collection of prepupae. Self-harvesting is further facilitated by the fact that BSF larvae are negatively phototactic and thus light can be used to encourage migration in desired directions upon user demand. The pupae stage generally lasts 9-20 days, and for example, 7-10 days depending on factors such as, for example, movement, proximity to other moving pupae, level of light, temperature and humidity, following which the adult fly will emerge. Adult BSFs mate and gravid female BSFs will lay eggs (i.e., “oviposit”) for the next generation. The life span of an adult BSF is generally 6-15 days, and, for example, 7-10 days, depending on humidity (e.g., 50-90%) and/or temperature (e.g., 22-35° C.) and stored energy, such as quantities and profiles of protein and fat. The timeline for the aforementioned life cycle is approximate and depends on environmental conditions and food supply. For example, it has been reported that limited food supply can extend the larval period to 4 months (Furman et al., 1959).
Under appropriate conditions, gravid female BSF adults will oviposit eggs approximately 24-72 hours after mating. Eggs are generally oviposited in tight, narrow spaces, such as blocks of cardboard with flutes oriented in any direction. Females are typically attracted to oviposition sites with pungent odours, as this usually indicates a potential food source for BSF offspring. BSF adults require specific environmental conditions to induce mating behaviors, including specific ranges of light, space, temperature and humidity. BSF will survive and mate at temperatures between 22° C. and 35° C. and humidity levels between 30% and 90%, and for example, BSF will survive and mate at an ambient air temperature of approximately 25° C.-30° C. with a relative humidity of approximately 60-80%. It has been reported that a BSF colony can be maintained at 22° C. (Tomberlin and Sheppard, 2002) and that the upper limit for optimal development of the BSF is between 30-36° C. (Tomberlin et al., 2009). A study measuring BSF mating and oviposition reported that 80% percent of egg clutches were deposited when humidity exceeded 60% (Tomberlin and Sheppard, 2002).
Direct sunlight has been reported to encourage mating (but not ovipositing) in BSF (Tomberlin and Sheppard, 2002). Accordingly, BSF mating is limited by weather conditions and time of year for non-tropical regions. Several artificial lights have been tested in lieu of sunlight. A 40 W Sylvania Gro Lux® (Orson Sylvania Inc., Danvers, Mass.) and a 430 W Pro Ultralight Light System® (Hydrofarm Inc. Petaluma, Calif.) were each reported to be unsuccessful in eliciting mating behavior (Tomberlin and Sheppard, 2002). Similarly, a 450 W (measured light intensity of 160 μmol·m−2·s−1, 50 cm below the bulb) rare earth light (Engineering University Infrared Technology Research Institute, Harbin, Heilung-Kiang China) reportedly failed to stimulate mating (Zhang et al., 2010). To date, the only artificial light source that has been reported to stimulate mating in BSF is a 500 W (measured light intensity of 160 μmol·m−2·s−1, 50 cm below the bulb) quartz-iodine lamp, which yielded 61.9% mating success compared to natural sunlight (Zhang et al., 2010).
Additionally, traditional BSF rearing systems consist of cages or greenhouses that require workers to enter or reach inside the cage with adults to add new prepupae to a pupation chamber, to collect eggs deposited on cardboard blocks, and to collect mortalities by sweeping or vacuuming. Requiring human workers to enter and exit the cage is disruptive because it allows flies to escape, disrupts mating behavior, potentially stresses flies by stimulating flight reactions and inadvertently leads to collecting live flies mortalities.